Digital Audio and the Mac
Digital Audio on the Internet
It’s all about bandwidth. As we recall from Part I of this series, the CD standard is 44.1KHz sampling rate and 16-bit sampling resolution. That means that at least 215,200 bits must be transmitted each second (44,100 16-bit words for both left and right channels) in order for the file to stream in real time. This rate of transfer is no problem either within a computer or among peripherals, but it far exceeds the baud rate of dialup modems (less than 56K).
What’s a Codec?
In order to transmit audio in real time, the bandwidth of the signal must be reduced to a low enough level to stream over an Internet connection. This reduction results in an unacceptable loss in quality unless the signal can be compressed. A codec (COmpression/DECompression) is a program that compresses an audio file to a small enough size to stream, then reconstructs the audio file on the other end. The more successful the codec, the closer the quality comes to the original and the fewer artifacts are present in the result.
RealPlayer began as Real Audio, the first proprietary audio codec intended specifically for the Internet. The company has since expanded into streaming video and evolved into Real Networks, the largest Internet entertainment provider. QuickTime and Microsoft’s Media Player are its two principal competitors.
A lot has been written lately about MP3, most of which deals with perceived threats of piracy. What makes MP3 (short for MPEG I Layer 3) such a threat is the combination of high quality and small size. The average MP3 file is only a tenth the size of the original CD quality file, reducing the size ratio from about 10 MB per minute (16-bit, 44.1KHz stereo) to 1 MB per minute. Though still too large to stream on a dialup modem, these files can be downloaded in a more reasonable size. And if you have a high-speed connection, such as a DSL or direct Ethernet connection, you can listen to these files in real time as you download them. As for the piracy concerns, technology will continue to develop and ultimately foil all attempts to prevent copying or encoding CD audio. Artists and businesses must adjust instead. (See my column in this month’s issue for more on this topic).
With a stake in the QuickTime format, it was no surprise that Apple would develop its own compression/decompression scheme for streaming audio and video. I heard a demonstration of its Q Design Audio codec last year at the SEAMUS (Society for Electro-Acoustic Music in the United States) conference in San Jose, California. The qualities of the Q Design-encoded and MP3-encoded files were comparable, though the examples provided were all from one composition (a contemporary work for string orchestra). I would have liked to hear a greater variety of examples. As a whole, I would give the Q Design codec high technical marks. Two issues I see though, are cost ($399 for the Q Design Pro encoder) and compatibility. Decoding the files requires QuickTime, which while universal in the Mac community, rates third in the PC community behind RealPlayer and Microsoft Media Player. MP3 files, in contrast, are universal.
What Happens Next?
Codecs will quickly hit the limit of smallest size at an acceptable quality. The Internet, however, will get faster and faster. Dialup modems will eventually disappear as the explosion of media on the Web demands greater bandwidth, and the Internet itself will be supplanted by a newer, faster version. Codecs might then become unnecessary, or perhaps just a leftover courtesy for tomorrow’s “slow” connections.
Update to Part III
Adaptec has recently announced the upgrade of both Toast and Toast Deluxe to version 4.1. This version promises Mac OS 9.0.x compatibility, though some users have reported problems. Adaptec claims that most of these problems arise from using the wrong updater, though they also admit to a few remaining issues, such as incompatibility with Multiple Users. However, a large number of frustrated users disagree with Adaptec’s claim, and have voiced their complaints loudly on sites such as MacInTouch and MacFixIt. Others report no problems at all. The only way to find out is to upgrade.
Update to Part IV
An upgrade to Mac OS 9 brings this inexpensive USB audio interface to new iMac, iBook, and PowerBook owners.
• • •
MIDIman has posted Mac drivers for three other PCI interfaces:
Pros: 4 analog ins and out (balanced or unbalanced), 24 bit/96KHz.
Cons: No digital ins or outs.
Pros: 6 analog ins and out (balanced or unbalanced), S/PDIF, 24 bit/96KHz.
Pros: 8 analog ins and out (balanced or unbalanced), MIDI, word clock, S/PDIF, 24 bit/96KHz.
Cons: S/PDIF stereo in and out only.
• • •
Here ends the Digital Audio and the Mac series. Keep an eye out for future updates.
Also in This Series
- Digital Audio on the Internet · June 2000
- Hardware · May 2000
- Software · April 2000
- The Specifics of Sampling · March 2000
- Fundamentals · February 2000
- Complete Archive
Reader Comments (1)
How do you calculate this. I can't figure it out how to get to 215.2Kbps.
44,100 samples/s * 16-bit * 2 channels = XXXMbps???
Lost in Space...
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